'\" te
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.TH KSTAT_QUEUE 9F "Aug 18, 2019"
.SH NAME
kstat_queue, kstat_waitq_enter, kstat_waitq_exit, kstat_runq_enter,
kstat_runq_exit, kstat_waitq_to_runq, kstat_runq_back_to_waitq \- update I/O
kstat statistics
.SH SYNOPSIS
.nf
#include <sys/types.h>
#include <sys/kstat.h>



\fBvoid\fR \fBkstat_waitq_enter\fR(\fBkstat_io_t *\fR\fIkiop\fR);
.fi

.LP
.nf
\fBvoid\fR \fBkstat_waitq_exit\fR(\fBkstat_io_t *\fR\fIkiop\fR);
.fi

.LP
.nf
\fBvoid\fR \fBkstat_runq_enter\fR(\fBkstat_io_t *\fR\fIkiop\fR);
.fi

.LP
.nf
\fBvoid\fR \fBkstat_runq_exit\fR(\fBkstat_io_t *\fR\fIkiop\fR);
.fi

.LP
.nf
\fBvoid\fR \fBkstat_waitq_to_runq\fR(\fBkstat_io_t *\fR\fIkiop\fR);
.fi

.LP
.nf
\fBvoid\fR \fBkstat_runq_back_to_waitq\fR(\fBkstat_io_t *\fR\fIkiop\fR);
.fi

.SH INTERFACE LEVEL
illumos DDI specific (illumos DDI)
.SH PARAMETERS
.ne 2
.na
\fB\fIkiop\fR \fR
.ad
.RS 9n
Pointer to a \fBkstat_io\fR(9S) structure.
.RE

.SH DESCRIPTION
A large number of \fBI/O\fR subsystems have at least two basic "lists" (or
queues) of transactions they manage: one for transactions that have been
accepted for processing but for which processing has yet to begin, and one for
transactions which are actively being processed (but not done). For this
reason, two cumulative time statistics are kept: wait (pre-service) time, and
run (service) time.
.sp
.LP
The \fBkstat_queue()\fR family of functions manage these times based on the
transitions between the driver wait queue and run queue.
.sp
.ne 2
.na
\fB\fBkstat_waitq_enter()\fR\fR
.ad
.RS 30n
\fBkstat_waitq_enter()\fR should be called when a request arrives and is placed
into a pre-service state (such as just prior to calling \fBdisksort\fR(9F)).
.RE

.sp
.ne 2
.na
\fB\fBkstat_waitq_exit()\fR\fR
.ad
.RS 30n
\fBkstat_waitq_exit()\fR should be used when a request is removed from its
pre-service state. (such as just prior to calling the driver's \fBstart\fR
routine).
.RE

.sp
.ne 2
.na
\fB\fBkstat_runq_enter()\fR\fR
.ad
.RS 30n
\fBkstat_runq_enter()\fR is also called when a request is placed in its service
state (just prior to calling the driver's start routine, but after
\fBkstat_waitq_exit()\fR).
.RE

.sp
.ne 2
.na
\fB\fBkstat_runq_exit()\fR\fR
.ad
.RS 30n
\fBkstat_runq_exit()\fR is used when a request is removed from its service
state (just prior to calling \fBbiodone\fR(9F)).
.RE

.sp
.ne 2
.na
\fB\fBkstat_waitq_to_runq()\fR\fR
.ad
.RS 30n
\fBkstat_waitq_to_runq()\fR transitions a request from the wait queue to the
run queue. This is useful wherever the driver would have normally done a
\fBkstat_waitq_exit()\fR followed by a call to \fBkstat_runq_enter()\fR.
.RE

.sp
.ne 2
.na
\fB\fBkstat_runq_back_to_waitq()\fR\fR
.ad
.RS 30n
\fBkstat_runq_back_to_waitq()\fR transitions a request from the run queue back
to the wait queue. This may be necessary in some cases (write throttling is an
example).
.RE

.SH RETURN VALUES
None.
.SH CONTEXT
The \fBkstat_queue()\fR family of functions can be called from user or kernel context.
.SH WARNINGS
These transitions must be protected by holding the \fBkstat\fR's \fBks_lock\fR,
and must be completely accurate (all transitions are recorded). Forgetting a
transition may, for example, make an idle disk appear 100% busy.
.SH SEE ALSO
.BR biodone (9F),
.BR disksort (9F),
.BR kstat_create (9F),
.BR kstat_delete (9F),
.BR kstat_named_init (9F),
.BR kstat (9S),
.BR kstat_io (9S)
.sp
.LP
\fIWriting Device Drivers\fR
